Impact Test:

Resistance of stones to impact is found by conducting tests in impacting testing machine .It contain of a frame with guides in which a metal hammer weighing 13.5 to15 kg may freely fall from a height of 380 mm.

                  Aggregate impact testing machine

Aggregates of size 10 mm to 12.5 mm range are filled in cylinder in three equal layers; each layer being tamped 25 times. Similar is then transferred to the cup and again tamped 25 times. The hammer is then permitted to fall freely on the specimen 15 times. The specimen is then sieved throughout 2.36 mm sieve. Then,

Where           

 W₂ = weight of fines

W₁ = original weight.

The recommended impact values for several works are:

• for wearing course >/30%
• for bituminous mechadam >/35%
• for water bound mechadam >/40%